Cooling fans are one of the main components in a cooling module. In recent years, with the trend that information products such as notebook computers and tablet personal computers are increasingly miniaturized and thinned and operation power of a processor thereof is greatly increased, a cooling module needs be miniaturized and thinned and have increased cooling efficiency. Therefore, a fan used by the cooling module must have a reduced volume, a reduced thickness, and an increased rotation speed. In order to satisfy the requirements for the miniaturization, thinning, and high rotation speed of the fan, many cooling fans currently use the design of hydrodynamic bearings in place of traditional bearings.
As shown in FIG. 8 and FIG. 9, a conventional cooling fan structure using a hydrodynamic bearing is shown. The cooling fan structure comprises a cooler housing 1, a bearing device 2 disposed on a bottom plate of the cooler housing 1, and a fan blade 3 disposed on an upper end of a rotation shaft 6 of the bearing device 2. A rotor 4 is further disposed on the fan blade 3 and a stator 5 is disposed on the bottom plate of the cooler housing 1. The rotor 4 and the stator 5 cooperate with each other to generate mutually exclusive magnetic fields for driving the fan blade 3 to rotate about the rotation shaft 6. As shown in FIG. 9, the bearing device 2 in the prior art includes: a housing 7, a hydrodynamic bearing 8 disposed in the housing 7, a compression ring 7a for fixing the hydrodynamic bearing 8 into the housing 7, and a rotation shaft 6 disposed through the hydrodynamic bearing 8.
The housing 7 has a cylindrical accommodating space therein. The hydrodynamic bearing is disposed in the accommodating space. A bottom plate 7b is integrally formed on a bottom of the housing 7 so that a closed space is formed between the accommodating space in the housing and a bottom surface of the hydrodynamic bearing 8, where the closed space is filled with a lubricating oil. A anti-friction pad 9 is disposed on a top surface of the bottom plate 7b and a bottom end of the rotation shaft 6 contacts a surface of the anti-friction pad 9 so that the bottom end of the rotation shaft 6 is supported by the bottom plate 7b. As shown in FIG. 9A, a herringbone groove 8a is disposed in a surface of an inner hole of the hydrodynamic bearing 8. The herringbone groove 8a functions to guide the lubricating oil to flow and pressing the lubricating oil when the rotation shaft 6 rotates. Therefore, an oil layer applied with pressure is formed between the rotation shaft 6 and the rotation shaft hole of the hydrodynamic bearing 8, so that the rotation shaft 6 will not contact a surface of the hydrodynamic bearing 8 when the fan operates, reducing a friction force during operation of the rotation shaft 6 and reducing abrasion of the hydrodynamic bearing 8 and the rotation shaft 6 during high-speed operation of the fan.
The main problem of the hydrodynamic bearing structure used for the conventional cooling fan is that, because the fan blade 3 has a very large diameter and the rotor 4 is disposed on the blade, vibration and deflection easily occur when the fan blade 3 operates, which results in not only vibration and noises in operation, but also abrasion of the rotation shaft 6 and the hydrodynamic bearing 8.
However, only radial support exists between the rotation shaft 6 and the hydrodynamic bearing 8 in the bearing device 2 without axial support, and an axial length of a joint between the rotation shaft 6 and the hydrodynamic bearing 8 is much less than the diameter of the cooling fan due to the flat design of the fan, so that support between the rotation shaft 6 and the hydrodynamic bearing 8 is insufficient, and thus the problem of the deflection and vibration during operation of the fan cannot be solved.
In addition, because the housing 7 of the bearing device 2 and the bottom plate on the bottom thereof are integrally formed, the rotation shaft 6 must be inserted into the hydrodynamic bearing 8 from an upper end of the hydrodynamic bearing 8 when the bearing device 2 is assembled, so that no additional positioning structure can be disposed on the rotation shaft 6, and thus the problem of insufficient support and positioning between the rotation shaft 6 and the hydrodynamic bearing 8 cannot be solved.
Furthermore, in the construction of the conventional bearing device 2, the anti-friction pad 9 disposed on the bottom of the housing 7 is a very thin sheet separated from the bottom plate 7b, so the anti-friction pad 9 is easily bent and deformed after being used for a long time.
In view of the above, the hydrodynamic bearing structure used for conventional cooling fans has many disadvantages. Therefore, it has become an important object in the art to improve operation stability of the hydrodynamic bearing structure used for conventional cooling fans to overcome the aforementioned disadvantages, through improvements in structural design.